jQuery ban url in textarea

HTML

<textarea required="required" name="message" id="message" rows="8" value="">s d sds d sdsd sd</textarea>

<br>

<button type="button" id="button">
submit
</button>

CSS

textarea.invalid { border: 1px solid red; }

JavaScript

$(document).ready(function(){
$("#button").click(function(){

var url = $("#message").val();
var b = url.search(/(?:https?|http):\/\/[\n\S]+/g);
if(b >0 ) {
alert("Textarea contains url")
} else {
 alert(b)
}

})

})